Breslow intermediates analogue

Stable Breslow intermediate analogues (23) derived from the reaction of chiral triazolylidene carbenes and iminium salts have been isolated. These structures are arguably the most relevant model systems for studying both asymmetric acyl anion reactivity and homoenolate reactivity. In solution, both olefin geometries are observed that can interconvert by two pathways. The isolation and analysis of these reactive species provides the most direct evidence for the role of Breslow intermediates in carbene catalysis. 

DiRocco, D. A., Oberg, K. M., Rovis, T. (2012). Isolable Analogues of the Breslow Intermediate Derived from... 

An overview of organocatalysis based on NHC yet avoiding the formation of a Breslow intermediate (acyl anion equivalent) has appeared. It encompasses the conjugate addition of carbenes, their addition to carboxylic acid derivatives as well as ketenes and analogues and illustrates the wide chemical diversity that can be achieved through these processes. 

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